This invention relates to the manufacture of printed circuit boards (PCBs) and especially to an improved process for making circuit boards of the solder-compatible type.
A circuit board of the general type to which the subject application relates is shown in U.S. Pat. No. 3,742,597. The PCB described therein is highly satisfactory but serious problems are encountered in the manufacturing process disclosed therein that tend to increase its cost and to reduce drastically the product yield. For example, the tolerances in matching electroconductive islands with preformed conductive terminal pads, without leaving gaps, proved to require excessive care. Moreover, the total number of processing steps assures that the resulting PCB must be undesirably expensive.
The general problem of manufacturing solder-compatible PCBs was then addressed by other inventors including Mack who describes a relatively complex method to overcome some of the problems inherent in the process disclosed in U.S. Pat. No. 4,104,111. Mack relied upon an extra tin/nickel coating to help assure dependable production of a suitable solder-bearing PCB. Further reference can be made to U.S. Pat. No. 4,104,111 for a good description of prior art relating to PCB manufacture.
Despite this earlier work, it has remained a problem to provide a solder-bearing PCB with a process which is, at once, both economic and dependable in that very close conductor lines may be formed and subjected to wave-soldering procedures to provide high-density, solder-compatible PCBs wherein a thin electroplated solder is used as a chemical resist during manufacture.